Impact of wind on secondary regulating power and energy in the Spanish system

The objective of this paper is to assess if high penetrations of wind power influence regulating secondary reserve requirements in the Spanish power system including three different topics: (i) needed ramps of variation of regulating power, (ii) amount of total regulating power and (iii) regulating energy. The results (both technical and economical) derived in this paper are based on the net load curve, defined as the difference between the load curve of the system and the wind generation curve. Since wind power does not provide yet secondary regulating reserve, net load represents the load that must be balanced by units providing the AGC service. Thus, the comparison of the three topics (ramps, regulating power and regulating energy) required by the net load with the ones required by the load curve represents the influence of wind on AGC requirements. Historical values of total demand and wind production with a 1 min resolution of the Spanish power system, collected for 2010 (when the wind share was close to 20%), are employed to derive significant conclusions. The analysis of this paper concludes that the main impact of wind in the Spanish system lies on the secondary regulating energy, while the required ramp rate and secondary reserve nearly not affected. Copyright © 2016 John Wiley & Sons, Ltd.     

Impact of wind power forecasting error bias on the economic operation of autonomous power systems

Many efforts have been presented in the literature for wind power forecasting in power systems and few of them have been used for autonomous power systems. In addition, some recent studies have evaluated the impact on the operation of power systems and energy markets that the improvement of wind power forecasting can have. In this paper, the value of the information provided to the operators of autonomous power systems about forecasting errors is studied. This information may vary significantly, e.g. it can be only the normalized mean absolute error of the forecast, or a probability density function of the errors for various levels of forecasted wind power, which can be provided either during the evaluation phase of the wind power forecasting tool or by online uncertainty estimators. This paper studies the impact of the level of detail provided about wind power forecasting accuracy for various levels of load and wind power production. The proposed analysis, when applied to the autonomous power system of Crete, shows significant changes among the various levels of information provided, not only in the operating cost but also in the wind power curtailment. Copyright © 2008 John Wiley & Sons, Ltd.     

On the wind power rejection in the islands of Crete and Rhodes

Crete and Rhodes represent the two biggest isolated power systems in Greece. The energy production in both islands is based on thermal power plants. The annual wind energy rejection percentage is calculated for Crete and Rhodes in this paper. The rejected wind energy is defined as the electric energy produced by the wind turbines and not absorbed by the utility network, mainly due to power production system's stability and dynamic security reasons. A parametric calculation of the annual wind energy rejection percentage, in terms of the installed wind power, the power demand and the maximum allowed wind power instant penetration percentage, is accomplished. The methodology takes into account (i) the wind power penetration probability, restricted by the thermal generators technical minima and the maximum allowed wind power instant penetration percentage over the instant power demand; and (ii) the wind power production probability, derived by the islands' wind potential. The present paper indicates that isolated power systems which are based on thermal power plants have a limited wind power installation capacity—in order to achieve and maintain an adequate level of system stability. For a maximum wind power instant penetration percentage of 30% of the power demand, in order to ensure an annual wind energy rejection percentage less than 10%, the total installed wind power should not exceed the 40% of the mean annual power demand. The results of this paper are applicable to medium and great size isolated power systems, with particular features: (i) the power production is based on thermal power plants; (ii) the power demand exhibits intensive seasonal variations and is uncorrelated to the wind data; (iii) the mean annual power demand is greater than 10MW; and (iv) a high wind potential, presenting mean annual wind velocity values greater than 7·5ms^?1, is recorded. Copyright © 2007 John Wiley &Sons, Ltd.     

Variability in large‐scale wind power generation

The paper demonstrates the characteristics of wind power variability and net load variability in multiple power systems based on real data from multiple years. Demonstrated characteristics include probability distribution for different ramp durations, seasonal and diurnal variability and low net load events. The comparison shows regions with low variability (Sweden, Spain and Germany), medium variability (Portugal, Ireland, Finland and Denmark) and regions with higher variability (Quebec, Bonneville Power Administration and Electric Reliability Council of Texas in North America; Gansu, Jilin and Liaoning in China; and Norway and offshore wind power in Denmark). For regions with low variability, the maximum 1 h wind ramps are below 10% of nominal capacity, and for regions with high variability, they may be close to 30%. Wind power variability is mainly explained by the extent of geographical spread, but also higher capacity factor causes higher variability. It was also shown how wind power ramps are autocorrelated and dependent on the operating output level. When wind power was concentrated in smaller area, there were outliers with high changes in wind output, which were not present in large areas with well‐dispersed wind power. Copyright © 2015 John Wiley & Sons, Ltd.     

Impact of hourly wind power variations on the system operation in the Nordic countries

The variations of wind power production will increase the flexibility needed in the system when significant amounts of load are covered by wind power. When studying the incremental effects that varying wind power production imposes on the power system, it is important to study the system as a whole: only the net imbalances have to be balanced by the system. Large geographical spreading of wind power will reduce variability, increase predictability and decrease the occasions with near zero or peak output. The goal of this work was to estimate the increase in hourly load‐following reserve requirements based on real wind power production and synchronous hourly load data in the four Nordic countries. The result is an increasing effect on reserve requirements with increasing wind power penetration. At a 10% penetration level (wind power production of gross demand) this is estimated as 1·5%–4% of installed wind capacity, taking into account that load variations are more predictable than wind power variations. Copyright © 2004 John Wiley & Sons, Ltd.     

Investigation on wind power potential on Hong Kong islands—an analysis of wind power and wind turbine characteristics

This paper discusses the potential for electricity generation on Hong Kong islands through an analysis of the local weather data and typical wind turbine characteristics. An optimum wind speed, u_op, is proposed to choose an optimal type of wind turbine for different weather conditions. A simulation model has been established to describe the characteristics of a particular wind turbine. A case study investigation allows wind speed and wind power density to be obtained using different hub heights, and the annual power generated by the wind turbine to be simulated. The wind turbine's capacity factor, being the ratio of actual annual power generation to the rated annual power generation, is shown to be 0.353, with the capacity factor in October as high as 0.50. The simulation shows the potential for wind power generation on the islands surrounding Hong Kong.     

Balance the wind power generation and transmission—case study in China

In most places in the world, the load center and the best wind resources are located far away from each other. Therefore, electricity generated from wind farms has to be transmitted to the load center over lengthy transmission lines. However, in some cases, lower quality wind resources also available close to load centers. Therefore, decision makers are sometime faced with competing alternatives: building wind farms in areas with higher wind speeds far away from load centers and or building wind farms in areas with lower wind speeds close to load centers. This paper proposes a methodology to help policy makers to develop wind resources cost effectively, balancing wind power generation from best wind resources and transmission of electricity over long distance. The methodology is applied to China, to compare development of high‐quality wind resources in the Three‐North region (north, northwest and northeast) and transmission of electricity to Southeast load centers to the development of lower quality resources closer to the same load centers. The results would help decision makers at the national and provincial levels to optimally develop the country's resources and assess the benefits of renewable energy trade between provinces. Copyright © 2015 John Wiley & Sons, Ltd.     

Maximum wind power generation in a power system imposed by system inertia and primary reserve requirements

Although the technology to simulate inertia or to provide primary control in wind power generators is mature, most of them are a source of power with neither inertia nor primary reserve provision mainly because it means wind spilling. Therefore, an increasing wind power penetration means a reduction in the inertia of the system and of the primary reserve due to the substitution of conventional generation. In this paper, the maximum wind power penetration focusing on system inertia and primary reserve value is assessed. The Spanish power system is used as an example for the calculation of these values. For this purpose, real Spanish scenario data are used. Results will show that high penetrations of wind power can be achieved without risking adequate values of primary reserve or inertia of the power system even if wind power does not contribute to these items. Copyright © 2014 John Wiley & Sons, Ltd.     

Robust multi‐model control of an autonomous wind power system

This article presents a robust multi‐model control structure for a wind power system that uses a variable speed wind turbine (VSWT) driving a permanent magnet synchronous generator (PMSG) connected to a local grid. The control problem consists in maximizing the energy captured from the wind for varying wind speeds. The VSWT‐PMSG linearized model analysis reveals the resonant nature of its dynamic at points on the optimal regimes characteristic (ORC). The natural frequency of the system and the damping factor are strongly dependent on the operating point on the ORC. Under these circumstances a robust multi‐model control structure is designed. The simulation results prove the viability of the proposed control structure. Copyright © 2006 John Wiley & Sons, Ltd.     

A new control methodology of wind turbine generators for frequency control of power system in isolated island

A wind turbine generator (WTG) system's output is not constant and fluctuates depending on wind conditions. Fluctuating power causes frequency deviations and adverse effects to an isolated power system when large output power from WTG systems is penetrated in the power system. This paper presents an output power control methodology of a WTG for frequency control using a load power estimator. The load power is estimated by a disturbance observer, and the output power command of the WTG is determined according to the estimated load. Besides, the WTG can also be controlled during wind turbulence since the output power command is determined by considering wind conditions. The reduction of the power system frequency deviation by using the WTG can be achieved by the proposed method. The effectiveness of the proposed method is validated by numerical simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

我国风力发电发展现状和问题分析

能源危机的日趋严重,优化能源结构、发展清洁环保的可再生能源迫在眉睫。风能是一种清洁环保的可再生能源,随着国家政策的支持和风力发电技术的不断发展,风力发电越来越得到人们的重视,并将在新能源发电中扮演重要的角色。概述了我国风能资源的储量和分布,介绍了近年来我国风力发电的总体情况、各省(自治区)风力发电的发展概况以及我国风电企业的发展现状,最后指出了我国风力发电目前出现的一些问题,并进行了分析。     

国内风力发电的现状和前景

分析了我国的风能资源和风力发电的现状，探讨了在风力发电时要注意的几个问题，并对我国风力发电的发展前景提出了看法。     

Survey of wind farm control—power and fatigue optimization

The main goal of this paper is to establish the present state of the art for wind farm control. The control area that will be focused on is the mechanical/aerodynamic part, which includes the wind turbines, their power production, fatigue and wakes affecting neighbouring wind turbines. The sub‐objectives in this area of research are as follows: (i) maximizing the total wind farm power production; (ii) following a reference for the total wind farm active power; and (iii) doing this in a manner that minimizes fatigue loading for the wind turbines in the farm. Each of these sub‐objectives is discussed, including the following important control issues: choice of input and output, control method and modelling used for controller design and simulation. The available literature from industry is also considered. Finally, a conclusion is presented discussing the established results, open challenges and necessary research. Copyright © 2014 John Wiley & Sons, Ltd.     

Simulating intra‐hourly wind power fluctuations on a power system level

In wind integration studies, sub‐hourly, load synchronous wind data are often preferable. These datasets can be generated by a hybrid approach, combining hourly measurements or output from meteorological models with a stochastic simulation of the high‐frequency fluctuations. This paper presents a method for simulating aggregated intra‐hourly wind power fluctuations for a power system, taking into account the time‐varying volatility seen in measurements. Some key elements in the modelling were transformations to stationarity, the use of frequency domain techniques including a search for appropriate phase angles and an adjustment of the resulting time series in order to get correct hourly means. Generation data from Denmark and Germany with 5 and 15 min temporal resolution were used for training models. It is shown that the distribution and non‐stationarity of simulated deviations from hourly means closely follow those of measurements. Power spectral densities and step change distributions agree well. Of particular importance is that the results are good also when the training and objective power systems are not the same. The computational cost is low in comparison with other approaches for generating high‐frequency data. Copyright © 2016 John Wiley & Sons, Ltd.     

Model‐based control addition to prescribe DFIG wind turbine fast frequency response

This paper investigates the physical capability of double‐fed induction generator (DFIG) wind turbines for inertial support of frequency response. Frequency stability is modeled using the DFIG electromechanical and generator controller dynamics, and a destabilizing effect is demonstrated in low‐inertia systems. To improve response, a synchronous reference frame DFIG controller is proposed that acts by following low‐frequency grid dynamics and adds a fast acting proportional plus integral (PI)‐controlled frequency‐responsive component to existing qd current commands. The proposed controller is derived in a straightforward manner using only the DFIG dynamic equations and is designed using pole/zero placement techniques. Laboratory experiments using a micro‐scale DFIG wind turbine with hub‐emulating flywheel prove better capability for transient frequency regulation even under extreme load change. The result is a DFIG controller that balances the appearance of transients in electrical and mechanical systems. Value is achieved in providing immediate continuous inertial response to support load change. The proposed frequency response can improve the use of existing physical inertia from wind turbines.     

风-水-火电互补系统中风电穿越功率的研究

针对风电容量与风-水-火电互补系统稳定性的关系问题,研究了风电机组的数学模型,搭建了风-水-火电互补系统的仿真模型.将遗传算法(GA)应用于风电穿越功率的研究,建立了基于遗传算法的风电容量的优化数学模型,构造了适值函数.对实际电网中的风电容量进行了优化编程计算和仿真,优化和仿真结果虽有差异,但很近似,验证了所建优化数学模型的合理性及遗传算法应用于风电穿越功率计算的可行性.     

直驱风电系统最大功率捕获技术的仿真分析

对直驱风电系统最大功率捕获技术进行了仿真分析.在仿真过程中,通过控制发电机组转速来实现风力机的最佳运行,使功率系数、风力机转速及输出机械功率等参数都能运行在不同风速下的最优值,从而最大限度地捕获风能.当发电机组达到最优运行时,再通过控制整流器使其输出恒定的电压.     

Dampening variations in wind power generation—the effect of optimizing geographic location of generating sites

This paper presents a method to dampen the variations in the output of aggregated wind power through geographic allocation of wind power generation sites. The method, which is based on the sequential optimization of site localization, is applied to the Nordic countries and Germany, using meteorologic wind speed data as the input. The results show that the variability in aggregated wind power output mitigates by applying sequential optimization. For the data used in this work, the coefficient of variation (standard deviation/mean) was 0.54 for the optimized aggregation of sites, as compared with 0.91 for the present day installation. An optimal allocation of wind power generation site reduces the need for dispatch and other measures to deal with the intermittent nature of wind power. Copyright © 2013 John Wiley & Sons, Ltd.     

Time series modelling of power output for large‐scale wind fleets

Simulations of power systems with high wind penetration need to represent the stochastic output of the wind farms. Many studies use historic wind data directly in the simulation. However, even if historic data are used to drive the realized wind output in scheduling simulations, a model of the wind's statistical properties may be needed to inform the commitment decisions for the dispatchable units. There are very few published studies that fit models to the power output of nation‐sized wind fleets rather than the output at a single location. We fitted a time series model to hourly, time‐averaged, aggregated wind power data from New Zealand, Denmark and Germany, based on univariate, second‐order autoregressive drivers. Our model is designed to reproduce the asymptotic distribution of power output, the diurnal variation and the volatility of power output over timescales up to several hours. For the cases examined here, it was also found to provide a generally good representation of the overall distribution of power output changes and the variation of volatility with power output level, as well as an acceptable representation of the distribution of calm periods. Copyright © 2011 John Wiley & Sons, Ltd.     

State modelling of self‐excited induction generator for wind power applications

The increase in wind power production with self‐excited induction generators (SEIGs) has led to new kinds of protection and stability problems. Suitable state models of a wind plant with SEIGs must accurately simulate balanced and unbalanced transient phenomena for adequate calibration and control of protection devices. However, the SEIG models currently available are unable to simulate the neutral current following unbalanced faults for forecasting the SEIG insulation and protection needed against some network stresses. In addition, the saturation model commonly used is not flexible when deriving a state model. This article presents an effective electromechanical state model for transient analysis of a saturated SEIG for wind power applications. A neutral connection through impedance is included for exact modelling of a Park wye‐connected SEIG. Simple‐shunt and short‐shunt (series) configurations are explored. A comparative analysis of the effects of these two types of configuration on the steady state and transient performances of an SEIG is presented. Numerical and experimental data obtained with a 380V, 5·5kVA, 11·9A, 50Hz induction generator are presented to attest to the effectiveness of the proposed SEIG modelling framework. Among the results obtained, simulations show that the simple‐shunt configuration produces poor voltage regulation, possible voltage collapse and inherent protection against short‐circuit faults, while the short‐shunt connection provides better voltage variation but needs to be well protected against short‐circuit faults. Copyright © 2006 John Wiley & Sons, Ltd.